Resistor assembly for circuit interrupters



5 Sheet-Sheet 1 B. P. BAKER ET AL INVENTORS Benjamin F. Baker and ErlingFrisch.

B B 28 7-uem75 B RESISTOR ASSEMBLY FOR CIRCUIT INTERRUPTERS March 17,1953 Filed March 4, 1950 WITNESSES:

March 17, 1953 B. P. BAKER ET AL 2, 32,97

RESISTOR ASSEMBLY FOR CIRCUIT INTERRUPTERS Filed March 4, 1950 3Sheets-Sheet 5 Fig.4. 34 F |g.5. 1

z 1 l E g l as as 35 ,l 32 l .6. U: J ;B

Fig.2

WITNESSES: INVENTOR Benjamin F? Baker W and Erling Frisch.

Patented Mar. 17, 1953 RESISTOR ASSEMBLY FOR, CIRCUIT INTERRUPTERSBenjamin P. Baker, Turtle Creek, and Erling Frisch, Pittsburgh, Pa.,assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application March 4, 1950, Serial No.147,734

9 Claims.

This invention relates to resistor assemblies, in general, and moreparticularly to an improved resistor assembly for use in a circuitinterrupter.

A general object of our invention is to provide an improved resistorassembly which will resist shock and which will be particularly suitablefor use in a circuit interrupter, particularly a circuit interrupter ofthe high voltage type.

A more specific object of our invention is to provide an improvedresistor assembly in which novel spring means are employed to maintainthe cast grid elements in proper position, yet permitting some expansionand contraction due not only to thermal stresses, but also due to thelarge repulsive magnetic forces involved by virtue of the fact thatlarge amperage currents may pass through the resistor assembly.

A further object of our invention is to provide an improved resistorassembly which will involve a minimum of space and which will not onlybe compact, but may be easily assembled by unskilled workmen.

Still a further object is to provide an improved resistor assemblyparticularly adapted for high voltage applications, and in which specialprovision is made for the prevention of flashover, or progressivecreepage breakdown between the resistor grid elements.

Still a further object is to provide an improved resistor assembly inwhich novel means are utilized for insuring good electrical contactbetween immediately adjacent resistor elements so that contact heatingmay be prevented, or at least greatly minimized.

Yet another object of our invention is to provide an improved resistorassembly utilizing novel spring means for maintaining the resistorelements in good contacting engagement, and also to provide means foreasily adjusting the spring pressure, not only when the assembly isinitially used in an installation, but also during the life of theassembly so that maintenance operations may be easily and quickly made.

A further object is to provide an improved resistor assembly in which aninsulating spacer plate separates immediately adjacent grid elements,and in which a suitable cement is employed, covering the two surfaces ofthe insulating spacer plate, which is baked following assembly oi theresistor elements. Such a construction, after bak ng, makes a more rigidresistor assembly which is not as susceptible to movement under theinfluence of high magnetic forces as would be the case if cement werenot used.

Further objects and advanta es will readily become apparent upon readingthe following specification taken in conjunction with the drawings, inwhich:

Figure 1 is a somewhat diagrammatic side elevational view, partly invertical section, of a circuit interrupter, particularly one of the highvoltage type, utilizing our improved resistor assembly, the contactstructure being shown in the closed-circuit position;

Fig. 2 is an enlarged top plan view of our improved resistor assembly;

Fig. 3 is a vertical sectional view taken along the line III-III of Fig.2;

Fig. 4 is a side vertical sectional view through our improved resistorassembly taken on the line IVIV of Fig. 2;

Fig. 5 is a plan view of one of the cast resistor elements;

Fig. 6 is an end elevational view of the resistor element shown in Fig.5;

Fig. 7 is a plan view of one of the insulating plates used in theconstruction of our improved resistor assembly;

Fig. 8 is atop plan view of one of the conducting spring washers;

Fig. 9 is a vertical sectional view taken through the spring washer ofFig. 8 along the line IX-IX thereof;

Fig. 10 is a plan view of one of the insulating washers used in theassembly of our improved resistor arrangement;

Fig. 11 is a vertical sectional view taken along the line m-on throughthe insulating washer of Fig. 10; and

Fig. 12 illustrates a modified construction similar to the constructionset forth in Figs. 1-11, inclusive, but shows in fragmentary fashion theuse of a suitable cement providing improved adherence between theresistor elements and the insulating spacing plate.

It will be apparent to those-skilled in the art that certain features ofour improved resistor assembly may be utilized in other types ofconstructions and installations other than those pertaining to circuitinterrupters. However, certain problems become more apparent, and mustbe given special attention, when the use of a resistor assembly isemployed in connection with a circuit interrupter, particularly acircuit interrupter oi the high voltage type in which vibration may be aconsiderable problem during the opening and closing operations and inwhich high amperage currents may be involved.

On compressed air circuit breakers of the orifice type, as well as thecross-blast type, it is well grid known that the interrupting capacitybreakers can be increased considerably by the use of shunting resistors.There are several methods available and well known to the art forinserting the resistor and interrupting the residual current. Onacross-blast type breaker, the resistance may be inserted by means of anauxiliary terminal in the arc chute which arcs over to the movingcontact when gases develop during interruption. then interrupted by thecontinued movement of the movable contact while Still in the area of theair blast. On a new 69 kv. orifice type breaker, presently to bedescribed, which has two series-connected contacts, the resistor .isconnected permanently across one contact, and the residual current isinterruptedbythe delayed opening of the second contact.

Referring to the drawings, and more particularly to Fig. 1 thereof, wehave disclosed one typical example of a circuit interrupter whichutilizes a resistor assembly to shunt a pair of contacts, and in which aseriallyconnected pair of contacts are utilized to interrupt theresidual current that will then pass through the resistor. Theinterrupter shown is of the compressed gas type adapted for high voltageapplication, such as 69 kv., but certain features of our invention areobviously usable in connection with other types of circuit interrupters,such as those adapted only for low voltage application.

The reference character l designates a or reservoir mounted on supports2, the latter resting upon a suitable foundation. Extendin upwardly in avertical direction from the tank 5 is a blast tube 3, of insulatingmaterial, wl supports an interrupter assembly, generally designated bythe reference character i. The interrupter assembly 4 comprises a pairof serially connected stationarycontacts 5, 6 and a pair of seriallyconnected cooperable movable contacts l, 8. The movable contacts "5, arebiased toward the closed position, as shown in l, by means of a pair ofcompression springs EB, 8B.

The movable contacts 1, 8 are supported in a movable contact assembly,generally designated by the reference character 9, and essen iallyincluding a pair of concentric cylinders 90 and iii. The separationbetween the cylinders 90 and 92' provides a substantially annular gasconduc ing space do which permits the ready flow of compressed gasupwardly through the blast tube 2i and to the movable contacts l, '8 sothat the latter may quickly be opened by the gas presure, but in adesired sequence. Obviously, the vable contacts I, B are separated awayfrom the stationary contacts 5, 6 against the opposition exerted by thecompression springs l3, during the existence of high pressureconditions.

When the gas pressure is lowered due to closingot the blast valve landleakage or" air occurs out of the interrupter assembly 4 "through theexpansion chambers 1!, 52 by virtue of the exhaust openings it providedtherein, the coinpression springs EB, 8B will serve to again close thecontact structure. However, this reclosure of the contact structureoccurs after the opening of the serially connected isolating switch M,as will be presently explained.

shunting the lower .set of contacts 5,, 'i is .a re stor assembly l5,including the resistance R, which carries the current between thecontacts and l after the latter have opened and the of the arctherebetween has been extinguished y he upwardly flowing gas blast- Theupper set of The residual current is 4 contacts as is purposely delayedin its op ning operation, so that at the time it is ope: i the lower arebetween the contacts 5 and l l already been extinguished, and at thistime the current passing through the interrupter will be traversing theresistor B.

As is well known by those skilled in art of circuit interruption, theuse of a shunting resistor R across the lower set of contacts "1 reducesthe amperage value of the current to interrupted, and also improves thepower factor, thereby making the upper are easier to inter As shown inFig. 1, the movable contact bly 9 is supported .by an insulating tubethe latter resting upon the expansion cha Her previously referred to.There is pron ed an orifice if? in the lower stationary contact i whichpermits the gas blast to pass therethrough ingthe opening operation.This gas blast, atter passing through the orifice H, and extinguish ingthe are between the contacts 5, l, pthe expansion chamber l2 by one ornore conduits E8 to collect within the expansion chamber "l2, and toraise the pressure therein. The purpose of raising the pressure withinthe ex pansion chamber i2 is to increase the dielectric strength of thegas adjacent the separated con tacts 5, l and also to cut .down theamount of gas flow.

In like manner, there :is provided the expansion chamber H at theupperend of the interrupter assembly .4, which rests upon a insulatingtube is, the tube 49 in turn rc upon the movable contact assembly '9.ably, a line terminal 20 :is associated with the upper expansion chamberH.

The compressed gas circuit interrupter, in Fig. 1, has an operatingmechanism enclosed within a housing 22 which serves to actuate aninsulating operating rod .23 at a pro er time :to effect iupwardswinging, or count rclockwise rotation, of the isolating switch lads itaway from the stationary disconnect cc; fingers 2 iassociated wi-th theterminal R1658";

disposed at the upper end of an in at tube 26, the latter beingsupported upon as ta '6. Also associated with the terminal memb is asecond line terminal 21, to which the ternalcircuit may be connected.

In the closed circuit position of the interrup ter, as shown in Fig. l,the electrical circuit passing *therethrough includes line terminalconducting expansion chamber H, stationary contact B, movable contact 8,inner cylinder 92' of the movable contact assembly 9, lower movablecontact l, stationary contact 5, through the conducting lower expansionchamber 52, and through the conducting isolating switch blade is to thestationary disconnect fingers 2t. and hence .to the other line terminal2! of the interrupter.

The blast valve l0, previously referred to, is of thedifferential-pressure type, being normally closed by an equalization ofthe gas pressure upon its two sides. A light spring 25 is provided tobias the blast valve Ill toward its closed posh .tion, but thespring 2.8is insufficient by itself to close the blast valve ill in opposition tothe pressure existing within the tank 5, which pressure may approach thevalue of 250 pounds per square inch. A valve controlling pipe 29 isprovided. to equalize the gas pressure on the two sides of thedifferential blast valve l0, and to effect the openingpf the blast valveIn by reducing the pressure therebeneath. The high pressure gas belowthe blast valve may be exhausted out through the .valve controlling pipe29 by suitable pneumatic valves, as well known by those skilled in theart.

Briefly, an opening operation of the interrupter disclosed in Fig. 1,includes an exhausting of the gas below the dilferential blast valve Illby the use of suitable pneumatic control equipment permitting suchexhausting to take place through the valve controlling pipe 29. Thedumping of such high pressure gas below the blast valve it permits thehigh pressure gas within the tank i to force the blast valve Illdownwardly in opposition to the light spring 28, and thereby permittingthe upward flow of compressed gas through the blast tube 3. This upwardflow of compressed gas first opens the lower set of contacts 5, l,suitable delaying means being provided (by suitable constricting actionupon the gas flow) so as to prevent immediate opening of the upper setof contacts 6, 8.

The initial opening of the lower set of contacts 5, l draws an are whichis extinguished by the gas flow passing between the contacts 5, l andexhausting through the orifice i? associated with the stationary contact5. This gas flow collects within the expansion chamber l2, despite theslight leakage through the exhaust opening 53, and the dielectricstrength of the gas adjacent the contact structure 5, i is improved, andthe flow of gas therebetween and out through the orifice i7 isdiminished by the rising gas pressure within the interior of the hollowstationary contact 5 and within the lower expansion chamber E2. Theshunting resistor R, shunting only the contacts 5, l, affords a parallelpath for the current flow, but the amperage of the current fiow isreduced by its passage through the resistor R.

Subsequently, the upper set of contacts 8, B are opened, and the gaspasses therebetween and out through an orifice Sll associated with theupper hollow stationary contact 6. This exhaust gas collects within theupper expansion chamber 5 i despite the bleeder opening it, with theresult that the gas pressure within the upper expansion chamber H rises,to improve the dielectric strength of the gas adjacent the upper contactstructure 6, 3, and also diminishes the quantity of gas passing outthrough the orifice 3% by virtue of the rising pressure within theexpansion chamber H and within the interior of the hollow stationarycontact 6.

The extinction of the upper are between the contacts it by the gas fiow,as previously described, breaks the residual current passing through theinterrupter. The circuit is then interrupted. Subsequently, the delayedaction of the operating mechanism 24 caused pneumaticcally by a delayedpassage of gas fiow through the conduit 34 into the mechanism 2! efiectsup- Ward counterclockwise swinging rotative motion of the isolatingswitch blade it away from the stationary disconnect contacts 24, toprovide thereby an isolating gap in the previously opened circuit.

Such an isolating gap permits the contact structure to be reclosed sincethe voltage will then be held by the isolating gap. In other words,following opening or" the isolating switch suitable means, not shown,effects high pressure gas flow upwardly through the valve controllingpipe 29 so that the pressurewill be equalized on both the top and bottomsides of the differential blast valve it. Since this pressure isequalized, the force exerted by the light compression spring 28 issufiicient to close the blast valve I0, and thereby halt the upward flowof compressed gas through the blast tube 3. The high pressure gas withinthe expansion chambers ll, l2 leaks out through the openings [3 so thatthe pressure adjacent the movable contact assembly 9 decreases, therebypermitting the compression springs 1B, SE to effect reclosure of thecontact structure, this all occurring following opening of thedisconnect switch M.

Certain features of the circuit interrupter disclosed in Fig. 1including a more elaborate description of the purpose of the shuntingresistor R are described and claimed in United States patent applicationSerial No. 74,406, filed February 3, 1949, now United States Patent2,627,- 005, issued January 27, 1953, to Benjamin P. Baker, ErlingFrisch, Wayne S. Aspey and John B. MacNeill, and assigned to theassignee of the instant application. Other features relating to theinterrupter assembly are described and claimed in United States patentapplication Serial No. 74,407, filed February 3, 1949, now United StatesPatent 2,602,868, issued July 8, 1952, to Benjamin P. Baker, ErlingFrisch and Howard M. Wilcox, and also assigned to the assignee of theinstant application. The pneumatic control for the aforementionedcompressed gas circuit interrupter, which is of the 69 kilovolt type, isdescribed and claimed in the United States patent application, SerialNo. 73,516, filed January 29, 1949, by Benjamin P. Baker and Howard M.Wilcox and likewise assigned to the assignee of the instant application.

We have found that for maximum efficiency the ohmic value of theresistor R must be quite low. On the particular 69 kilovolt breaker,heretofore described, the ohmic value was 12 ohms to obtain the desiredinterrupting capacity. With this resistor, the residual current reachesa maximum value of 3,700 amperes based on 44 kilovolts phase-to-groundvoltage.

The design of a resistor for this type of service presents severalproblems not ordinarily en countered in the design of resistors forother purposes. In the first place, the resistor must be adequatelyinsulated for the high voltage, while occupying minimum space, Moreover,the resistor elements must be securely braced to prevent shifting andpossible flashovers between the resistor elements as a result of thelarge magnetic forces developed by the high currents duringinterruption. While the resistor must carry heavy short-circuitcurrents, it is required to carry current for only the very short timerequired to open the circuit interrupter and extin guish the arc. Inaddition, it is desirable to make the resistor such that it will be easyto assemble in the shop by unskilled workmen, and moreover beingassembled without the use of welding or soldering.

Referring to Figs. 5 and 6, there is shown one of the grid resistorelements 32, which is preferably cast out of a suitable metal, whichwill not only have a high specific resistance but will able to withstandthe shock and concussion caused by the opening and closing of theinterrupter of Fig. 1. It will be observed that the zigzag turns 33 ofthe resistor element 32 are extended laterally to such an extent thatthey come approximately along the same outer lines 33' as is defined bythe'lug portions 34. It will also be observed that the lug portions 34have relatively large apertures or openings 35 provided therethrough,the purpose for which will appear more clearly hereinafter. Further, itwill the result be observed that the "lug portions "34 take space 34'which is provided by shorter turns 338 'so that is a substantiallyrectangularly shapedresistor element, as clearly shown in Fig. '5,providing the maximum resistance area with the minimum surface area.

Referring to Fig. 6, which shows an end elevational View of the resistorelement 32, it will be observed that the lug portions 3 5 do not rise,or are not elevated or depressed, above or below the planes of the turns33, or in other words, no elevated or depressed bosses are formed by thelug portions 34. This has the advantage that in assembling the resistorelements 32 a maximum'number of such elements 32 may be stacked with aminimum longitudinal space along the stack. If the lug portions 3d wereraised, or formed bosses, with respect 'to the plane of the turns '33,there would clearly be a fewer number of such grids 32 assembled for thesame amount of longitudinal space, as compared to the former case inwhich the lug portions 3' 3 are exactly on a level with'the turns 33 ofthe element 34. Further advantages will be set forth later.

Referring to Fig. 7, there is shown a plan view of one of the insulatingplates provided between each of the resistor elements 32. This plate orplate portion is designated by the reference numeral "36, and ispreferably made of a highly insulating material which is not susceptibleto breakage or to thermal deterioration. We have found mica to be sucha. suitable material. It will be noted that there "is provided in themica plate '35 an aperture or opening 3? and a cutout portion 38 at thediagonal corners of the plate 36, the purpose for which will be moreclearly explained hereinafter.

Referring to Figs. 8 and 9, attention is directed to the conductingspring washers 353, which are insulating plate 36, the purpose for whichwill be subsequently explained. However, it will be observed that theconcave shape id of the spring washer 39 is such that the thickness S asindicated in Fig. 9, is greater than the thickness o the mica plate 36.

Referring to Figs. 2, 3 and 4, it will be apparent that the resistorassembly l5 utilizes a pair of end castings i2, it. The upper casting 52has a laterally extending bracket portion it with a plurality ofapertures (Fig. 4) extending therethrough, so that in the assembledposition of the resistor assembly I 5, as viewed in Fig. 1, suitablebolts may be utilized, passing through the apertures es of the bracket Mto secure the upper end of the resistor assembly to the outer cylinderto of the movable contact assembly e, as at ti. Thus, there is providedgood physical securement, and also good electrical engagement betweenthe upper end of the resistor assembly 55 and the movable contactassembly .l.

The lower casting has a pair of threaded holes provided therein so thatsuitable bolts may secure the lower casting it to the lower conductingmetallic expansion chamber iii or Fig. 1, as at 59.

8 The result is good physical attachment of the lower end of theresistor assembly E5 to the expansion chamber 12, and also goodelectrical contact being provided therebetween.

The lower casting ts also has a pair of apertured lug portions ll whichare internally threaded to receive a pair of metallic studs 48, thelatter being suitably secured to the lower ends of a pair of insulatingguide rods 9. In the assembling operations, the first'step is tothreadedly secure the guide rods fit into the lower easting #53. Thegrid elements are then placed upon the guide rods is so that the guiderods it pass through the apertures 35 of the lugs 35 of the resistorelements 32. Between adjacent resistor elements 32 are disposed the micaplates 36, alternately placed so that the cutout portion 33 of the micaplate 3S occurs at the place where the lugs 34 of the elements 32 are tobe electrically connected. The aperture 8? of the mica plate at is justlarge enough to receive the guide rod 49 at the unconnected end of thegrids 321.

Between the lug portions 3%, which are to be electrically connected,adjacent the cutout por tion 38 of the plate 36,, a Phosphor bronzespring washer 35, previously described in connection with Figs. 3 and 9,is utilized. Also, wherever the spring washer 39 is utilized, aninsulating washer ii! is employed within the spring washer, the purposefor which will appear more fully here inafter.

Fig. 3 shows more clearly the assembling steps taken to insure goodinsulating connections and good electrical connections. As shown in Fig.3, the mica plates 33 extend beyond the edges of the grids 3'2 and thusprovide a long creepage path having a breakdown voltage considerably inexcess of the requirements for the voltage rating. lhe mica plates 35have sui'ficient thickness to insulate substantially the whole surfacearea of each element 32 from its neighbor.

As shown, the resistor stack 35 is supported between the two castings3'2 and which are secured together by two insulating straps t2. Bolts 53and nuts E i rigidly secure the castings d2, E3, to the spacing straps52, as shown more clearly in Fig. 3. In order to prevent shifting of thegrids or resistor elements 32, they are compressed evenly over theirentire surface area by means of eight heavy springs which, in theparticular instance concerned with, produce a total pressure in theneighborhood of 1,909 to 2,006 pounds. The springs are loaded by meansof two set screws 55, which threadedly pass through the upper casting t2and bear upon an upper steel spring plate El. The lower ends of thecompression springs 55 bear upon a brass spring plate 58 having notches58 for ventilation. The brass spring plate 58 preferably has a pluralityof screws 59 passing therethrough, as shown in Fig. 3, with a pluralityof washers it surrounding the upper shank portion of the screw 59, witha nut El threaded thereupon. The purpose of the screws, washers and nuts5:2 58 and 65 is to provide a lower spring seat for the compressionspring 55, so that there will not take place any lateral movement of thespring 55 to change its position due to vibration of the inter rupter.

To insure good contacting engagement between the lower spring plate 58and the upper spring plate bl, we provide a pair of conducting straps 63having a pair of apertures at their outer ends. One-of the aperturesreceives the screw as and is pressed against the lower spring plate 58by the lower end of one of the compression springs 55, as shown moreclearly in Fig. 3. The other aperture in the conducting strap 63receives the upper end of the guide rod 49 and is pressed against theupper spring plate by a metallic spacing tube 64, as shown more clearlyin Fig. 4. The two conducting straps 63 are disposed at opposite ends ofthe resistor assembly l5, as more clearly shown in Fig. 2.

The electrical circuit passing through the resistor R. of the assemblyl5 hence comprises the top casting 42, the set screws 53, the upperspring plate 5?, conducting straps 83, lower spring plate 58, Phosphorbronze washer 39 (left-hand side of Fig. 3), left lug 34 of the topresistor element 32 (Fig. 3), thence through the turns 33 of the topresistor grid 32 to the right-hand lug 94 of 3. The circuit then extendsthrough another spring washer 39 to the lug portion 33 of the secondresistor element 32 and so on in a zigzag path down to the right lug 34of the lowermost resistor element 33 of Fig. l. Since there is provideda mica plate 35 below the lowermost resistor ele ment 32, as shown inFig. 4, again resort is had to a spring washer 39 (right-hand side ofFig. 4) to conduct the current from the lug portion at of the lowermostresistor element 32 to the lower conducting casting 43. The circuit thenextends through the bolts, not shown, which secure the lower casting 43to the expansion chamber i2 (Fig. 1), and thence to the lower stationarycontact 5.

The lower casting 43 is also provided with a laterally extending bracketportion 65 which is drilled and tapped to receive bolts 66 which securean insulating rectangularly-shaped housing 61 to the resistor assemblyl5. However, there is provided space, such as at 68, between the lowercasting 43 and the inner surface of the housing 31 so as to permit freecirculation of air upwardly through the interior of the housing 6? andthereby pass the several grids 32 and notches 53' of spring plate 58.

The lower spring plate 58 is preferably made of a relatively thinmaterial with sufficient flexibility, such as brass, to distribute thespring pressure evenly upon the grids 32. As mentioned, the grids 32 aremade of a special alloy which hasa very high specific resistance and issufficiently ductile to be shockproof. Preferably, also the grids 32 aremade free of projections which might puncture the mica insulating plates36 and thereby prevent even distribution of pressure from grid to grid.

The assembling operations will now be described. The grids and the micainsulating plates 36 are assembled upon the bottom casting 43 with theinsulating tie rods 49 projecting upwardly from the lower casting 43 andfitting into the guide holes 35 provided in the grids 32. The tie rods49 likewise serve to locate the mica plates 36. The grids areelectrically connected in series by placing the Phosphor bronze washers39 between alternate terminals of adjacent grids. The large hole orcutout 38 in the plate 33 at this point permits insertion of the washers39. The spring washers 39 are made of a slightly thinner material thanthe mica plates 36 to obtain good contact pressure, and at the same timeto prevent the washers 39 from going solid and therebypreventing'distribution of pressure on the rest of the grid surface,which would be the insulating spacers 5|, placed inside the washers 39and the holes 35 in the resistor grids 32, serve to give sufficientinsulation creepage path between non-connected grids 32 around the tierods 49.

The complete assembly, including the springs and the upper and lowerspring plates 57, 58 are held together temporarily by tightening the tierod nuts 69 (Fig. 3) to obtain a slight tension in the tie rods 49. Thenuts 69 thread upon short stud lengths 49 secured to the upper end orthe tie rods 49. After the insulating straps 52 and upper casting 42have been assembled, the springs 33 are compressed to final loading bymeans of the set screws 56. Correct loading is obtained by compressingthe springs 55 to a length determined by the metallic spacer tubes 64,as

shown more clearly in Fig. 3. As shown, the spacer tubes 64 are disposedaround the tie rods 49 between the two spring loading plates 51, 58.

The rectangular insulating shield or housing 61 covers the resistorassembly l5 and protects it from damage. The air spacing between thegrids 32 and the cover 61 permits free circulation of cooling air aboutthe grids 32.

From the foregoing description of our improved resistor assembly, itwill be apparent that we have provided a novel means of stacking fiatcast grids 32 and mica plates 36 under pressure to obtain adequateinsulation with a minimum space factor and to permit bracing of thegrids 32. The use of the spring washers 39 provides good contact betweenadjacent grids 32, and the two insulating guide rods 49 provide a simpleguide means for locating the grids 32 and the mica plates 36 during thestacking operation and to hold the grid assembly l5 together until finalpressure is applied by tightening the set screws 56. The tie rods 49also prevent shifting of the grids 32 and of the plates 36 on thecompleted resistor assembly.

It will moreover be apparent that we have provided bracing of the grids32 by applying a high even pressure over the entire surface by means ofa number of compression springs 55.

Fig. 12 shows a modification of our invention in which a suitable cement73 is employed covering the two surfaces of the insulating mica plate 33to provide improved adherence between the resistor elements 32 and themica plate 36. In order to prevent motion of the zigzag grids 32 underthe influence of the magnetic forces, it was found desirable to providegreater adhesion between the grids 32 and the mica spacer 36 than couldbe provided by pressure alone. In order to do this, we painted the topand bottom surfaces of the mica plate 36 with a cement, such as aurea-formaldehyde cement, and following assembly of the resistorelements 32 baked the entire assembly I5 for several hours. This cement73, as shown in Fig. 12, stuck the grids 32 to the mica plate 35, andthe excess cement was squeezed out forming a spacer 14 between thezigzag turns 33. The entire structure was, therefore, much more solidand stronger to resist magnetic forces and mechanical shock.

Although we have described our invention as particularly applied to ahigh voltage compressed air circuit interrupter, it will be apparent tothose skilled in the art that certain features of our invention areapplicabl wherever resistor as semblies may be utilized. Merely for thepurposes of illustration have we disclosed our improved resistor asapplied to a high voltage compressed gas circuit interrupter.

resistor element having one or more apertured lug portion the'two sidesof each lug portion or each resistor element being in the same'planes asthe two sides of the turns, one or more insulated tie 'rods passingthrough the apertured lug per: t'io'ns, an insulating spacer platedisposed betwe en immediately adjacent resistor elementssov asto'cove'r' a substantial portion of the area. or the resistor elements,resilient means for applying a resilient pressure over the resistorelements in their assembled state, a resilient. springlwasher eontfresis'tance therebetween, each suchspring washer having" an expandedthickness greater than that of the insulating plate, and acontracted7thicknes's less than that of the. insulating at M.

' "Z'IA resistor assembly including a plurality of fiat plate-likeresistorelements, eachsuch resistor element having a plurality of turns,each resis or.

element haying, one or more apertured lug portions, the two sides ofeach his portion of each resistorelement being in the same planes asthe,

two" sides of the turns, one or more insulated tie rods passing throughthe apertured lug portions, aniinsulating. spacer plate disposed betweeninornediat'ely adjacent resistor elements so as to never a substantialportion of the area of the resistor elements, resilient means forapplying. av

resilient pressure over the resistor elements in their assembled state,a resilientspring washer between contacting lug portions for loweringthe,

contact resistance .therebetween, each such spring washer having anexpanded thickness greater than that of the insulating plate, acontracted thicknessless than that of the insulating plate,

an. i'nsulating, Washer disposed inside of each springwashenconsideringa sectionbetween the, ends of the resistor assembly,encircling the tie rod and disposedwithinthe apertures of adjacentcontacting lug portions to give, sufficient insulating creepage betweennon-connectedresistorelements around the tie rod.

'BQA circuit interrupter including aresistor assembly. including aplurality of flat plate-lilze resistor elements, each such resistorelement hav- 7 mg "a plurality of turns, each resistor element havingone or more apertured lug portions, the twofsi'ld'es of each. lugportion of each resistor elenieht, being, in the same planes as the twosides oi the turns, one or more insulated tie rods passing throughtheapertured lug portions, an insulating'spacer plate disposed betweenimmediately adjacent resistor elements so as to cover, a substantialportion of the area of the resistor elements, resilient means forapplying a pressure over the resistor elements in their assembled state,a resilient spring washer between contacting lug portions for loweringthe contact resistance therebetween, each such spring washer having anexpanded thickness greater than that of the in sulating plate, and acontracted thickness less than that of the insulating plate,

45A circuit interrupter including a resistor asbetween contactinglugpo'rtion r:- lowering the 12 sembly. including a plurality of fiat.plate-Hiram: sistor elen1ents,'each such resistor elementhaving, aplurality of turns, each resistor elfimfint'haying. one or moreapertured lug portions, thetwo sides. or" each lug portion of eachresistor element b ing in the same planes as the two sides, of.theturns; one or more insulated tie, rods passin through the aperturedlug portions, an insulating spacer plate disposed between immediately.adjacent, re-. sistor elements so as to cover a subs tantial.por-, tionof the area of the resistor elements, resilient means for applying apressure over theresistor elements in their assembled state, aresilient. spring washer between contacting lug portions, for loweringthe contact resistance therebetween, each such spring washer. having anexpanded. thickness greater than that of the insulating plate, acontracted thicknessless than thatof the. insulating plate, and aninsulatingv Washer disposed inside of each spring washer, considering.

a section between the endsof the resistor assemw.

bly, encircling the tie rod and. disposedwithinthe apertures of adjacentcontacting lug portions to give suflicient insulating creepag'el'ietv-Jeenv nonconnected resistor elements around the tie rod, 5. Aresistor assembly including. apluralityof.

ence between the insulatingspacer plate. and .one

of the resistor elements immediately. adjacen'tto thecoatedsuriace ofthe insulating spacer plate. 6. Aresistor assembly including. a.-plurality.. .of

flat plate-like resistor elements, eachtsulchresistors element having apluralityof turns, an, insulating} spacer plate. disposed betweenimmediately. adj a-.,' cent resistor elements so asto cover asubstantial, portion of the area oftheresistor elements, and

a cement. coating on at least one side I oifthe', in: sulating spacerplate, to provide'greater. adherence between the insulating.spacerplateand one of the resistor elementsirnmediately,adjacentito thecoatedsurface of, theinsulating spacer. plate, and,means ,for applying.apressuite over the res, sistor elements in their assembledjform;

'7. A resistor assembly includinga'plurality of flat, plate-likeresistor elements, each such resistor element having, aplurality of.turns, each resistor element havingone. or morelugeportionsf withopenings. therethrough, one,v or more;v m, sulated tie rods passingthrough the lugtportionsg an insulating plate portionbetween.adjacent-resister elements, and, aresilient spring washer be;

tween contacting, lug. portions. fo loweringathe. contact resistancetherebetweemcach such springf washer having.v an expandedthicknessgreaten thanthat of theinsulatingplateportion, and a contractedthickness .lessthanthat of the insulating plateportion.

8, A resistor assembly including resistor" ole-1 mentshav'ing fiat lug.portions with openings therethrough, at least: one of said lug, portionsbe:

ing connected to thenext adjacent lug portion on: 7 one. sideandunconnected ironrthe adjacent lug portionon the otherv side,. a tie rodwith an external insulating surface passing through the open: ingsin theflat. lug portions or the resistorelea men'ts, one .or more insulatingwasheracertainsoi. the openings in the connected lusportionsbeing largerthan thetie rodto accommodate one :01" said insulating. washerstherein,- an insulating plate portion with an opening therethrough ofonly slightly larger dimension than the tie rod but smaller than saidlarger openings, a resistor element on the other side of the insulatingplate portion having a lug portion unconnected with the lug portion ofthe next adjacent resistor element, and said insulating Washermaintaining the edges of said larger openings in the flat connected lugportions away from the smaller opening in the insulating plate portionto give sufiicient insulation creepage between the connected andnon-connected lug portions of the resistor elements.

9. A resistor assembly including a plurality oi flat plate-like resistorelements, each such resistor element having a plurality of turns, aninsulating spacer plate disposed between immediately adjacent resistorelements so as to cover a substantial portion of the area of theresistor elements, and a cement coating on both sides of the insulatingspacer plate, to provide greater adherence between the insulating spacerplate and both of the resistor elements immediately adjacent to thecoated surfaces of the insulating spacer plate.

BENJAMIN P. BAKER. ERLING FRISCH.

REFERENCES CITED The following references are of record in the file ofthis patent:

